From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: References: <20210210091445.741269-1-olteanv@gmail.com> <20210210091445.741269-9-olteanv@gmail.com> From: Nikolay Aleksandrov Message-ID: <0208ba7c-601b-de5c-1922-c6d1911501a1@nvidia.com> Date: Wed, 10 Feb 2021 12:14:06 +0200 In-Reply-To: <20210210091445.741269-9-olteanv@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit MIME-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1612952073; bh=zgUy/wru6f2nYcJA3qXWcQJ2f3n/Oyblho3aFWygJk4=; h=ARC-Seal:ARC-Message-Signature:ARC-Authentication-Results: Authentication-Results:Subject:To:CC:References:From:Message-ID: Date:User-Agent:In-Reply-To:Content-Type:Content-Language: Content-Transfer-Encoding:X-Originating-IP:X-ClientProxiedBy: MIME-Version:X-MS-Exchange-MessageSentRepresentingType: X-MS-PublicTrafficType:X-MS-Office365-Filtering-Correlation-Id: X-MS-TrafficTypeDiagnostic:X-MS-Exchange-Transport-Forked: X-Microsoft-Antispam-PRVS:X-Header:X-MS-Oob-TLC-OOBClassifiers: X-MS-Exchange-SenderADCheck:X-Microsoft-Antispam: X-Microsoft-Antispam-Message-Info:X-Forefront-Antispam-Report: X-MS-Exchange-AntiSpam-MessageData: X-MS-Exchange-CrossTenant-Network-Message-Id: X-MS-Exchange-CrossTenant-AuthSource: X-MS-Exchange-CrossTenant-AuthAs: X-MS-Exchange-CrossTenant-OriginalArrivalTime: X-MS-Exchange-CrossTenant-FromEntityHeader: X-MS-Exchange-CrossTenant-Id:X-MS-Exchange-CrossTenant-MailboxType: X-MS-Exchange-CrossTenant-UserPrincipalName: X-MS-Exchange-Transport-CrossTenantHeadersStamped:X-OriginatorOrg; b=ZtOfmDlfV1Tp7N8HhlFgU4zJwdGshYQQCmepadE+GqO0WjdXzgyrQlQ5KEV/a/sf7 zTqggHdYQSa4HVyCs0RgDjmPELGcwDV49Ukl6u7vYWmMeHrRgjQ7D4wVRm/6kjIV84 Rps2/5Uk48WpUvBG9czEJv+8CDNqccQ3qS5lLnJ7gp9o0hnoH8kYpywHwXCmgKjl24 LY1SiaUvKM60RK6PlQ3UJkj5CJdozIoxbMxsXZHj5GOvfjJH1ZV/QD+Rf5aYhTY/wk nBe/0yCaPB7kksI4amfn7SmngDldSOICG7Y5T4HTBOKhb4sIeSiedesXHGrpgxrrd+ rXdkaUbGIY1XA== Subject: Re: [Bridge] [PATCH v3 net-next 08/11] net: bridge: put SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS on the blocking call chain List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladimir Oltean , Jakub Kicinski , "David S. Miller" Cc: Ivan Vecera , Andrew Lunn , Alexandre Belloni , Florian Fainelli , Jiri Pirko , Vadym Kochan , netdev@vger.kernel.org, bridge@lists.linux-foundation.org, Ioana Ciornei , linux-kernel@vger.kernel.org, UNGLinuxDriver@microchip.com, Taras Chornyi , Ido Schimmel , Claudiu Manoil , Grygorii Strashko , Roopa Prabhu , linux-omap@vger.kernel.org, Vivien Didelot On 10/02/2021 11:14, Vladimir Oltean wrote: > From: Vladimir Oltean > > Since we would like br_switchdev_set_port_flag to not use an atomic > notifier, it should be called from outside spinlock context. > > We can temporarily drop br->lock, but that creates some concurrency > complications (example below is given for sysfs): > - There might be an "echo 1 > multicast_flood" simultaneous with an > "echo 0 > multicast_flood". The result of this is nondeterministic > either way, so I'm not too concerned as long as the result is > consistent (no other flags have changed). > - There might be an "echo 1 > multicast_flood" simultaneous with an > "echo 0 > learning". My expectation is that none of the two writes are > "eaten", and the final flags contain BR_MCAST_FLOOD=1 and BR_LEARNING=0 > regardless of the order of execution. That is actually possible if, on > the commit path, we don't do a trivial "p->flags = flags" which might > overwrite bits outside of our mask, but instead we just change the > flags corresponding to our mask. > Not sure I follow here, how do we get any concurrency issues with sysfs or netlink when both take rtnl before doing any changes ? > Now that br_switchdev_set_port_flag is never called from under br->lock, > it runs in sleepable context. > > All switchdev drivers handle SWITCHDEV_PORT_ATTR_SET as both blocking > and atomic, so no changes are needed on that front. > > Signed-off-by: Vladimir Oltean > --- > Changes in v3: > - Drop the br->lock around br_switchdev_set_port_flag in this patch, for > both sysfs and netlink. > - Only set/restore the masked bits in p->flags to avoid concurrency > issues. > > Changes in v2: > Patch is new. > > net/bridge/br_netlink.c | 10 +++++++--- > net/bridge/br_switchdev.c | 5 ++--- > net/bridge/br_sysfs_if.c | 22 ++++++++++++++-------- > 3 files changed, 23 insertions(+), 14 deletions(-) > > diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c > index b7731614c036..8f09106966c4 100644 > --- a/net/bridge/br_netlink.c > +++ b/net/bridge/br_netlink.c > @@ -869,7 +869,7 @@ static void br_set_port_flag(struct net_bridge_port *p, struct nlattr *tb[], > static int br_setport(struct net_bridge_port *p, struct nlattr *tb[], > struct netlink_ext_ack *extack) > { > - unsigned long old_flags, changed_mask; > + unsigned long flags, old_flags, changed_mask; > bool br_vlan_tunnel_old; > int err; > > @@ -896,10 +896,14 @@ static int br_setport(struct net_bridge_port *p, struct nlattr *tb[], > br_set_port_flag(p, tb, IFLA_BRPORT_ISOLATED, BR_ISOLATED); > > changed_mask = old_flags ^ p->flags; > + flags = p->flags; > > - err = br_switchdev_set_port_flag(p, p->flags, changed_mask, extack); > + spin_unlock_bh(&p->br->lock); > + err = br_switchdev_set_port_flag(p, flags, changed_mask, extack); > + spin_lock_bh(&p->br->lock); > if (err) { > - p->flags = old_flags; > + p->flags &= ~changed_mask; > + p->flags |= (old_flags & changed_mask); > goto out; > } > > diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c > index dbd94156960f..a79164ee65b9 100644 > --- a/net/bridge/br_switchdev.c > +++ b/net/bridge/br_switchdev.c > @@ -79,9 +79,8 @@ int br_switchdev_set_port_flag(struct net_bridge_port *p, > attr.u.brport_flags.val = flags & mask; > attr.u.brport_flags.mask = mask; > > - /* We run from atomic context here */ > - err = call_switchdev_notifiers(SWITCHDEV_PORT_ATTR_SET, p->dev, > - &info.info, extack); > + err = call_switchdev_blocking_notifiers(SWITCHDEV_PORT_ATTR_SET, p->dev, > + &info.info, extack); > err = notifier_to_errno(err); > if (err == -EOPNOTSUPP) > return 0; > diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c > index 72e92376eef1..3f21fdd1cdaa 100644 > --- a/net/bridge/br_sysfs_if.c > +++ b/net/bridge/br_sysfs_if.c > @@ -68,16 +68,22 @@ static int store_flag(struct net_bridge_port *p, unsigned long v, > else > flags &= ~mask; > > - if (flags != p->flags) { > - err = br_switchdev_set_port_flag(p, flags, mask, &extack); > - if (err) { > - netdev_err(p->dev, "%s\n", extack._msg); > - return err; > - } > + if (flags == p->flags) > + return 0; > > - p->flags = flags; > - br_port_flags_change(p, mask); > + spin_unlock_bh(&p->br->lock); > + err = br_switchdev_set_port_flag(p, flags, mask, &extack); > + spin_lock_bh(&p->br->lock); > + if (err) { > + netdev_err(p->dev, "%s\n", extack._msg); > + return err; > } > + > + p->flags &= ~mask; > + p->flags |= (flags & mask); > + > + br_port_flags_change(p, mask); > + > return 0; > } > >